A web document is an electronic document that is suitable for use with a web browser. Web documents are identified by Uniform Resource Identifiers (UIRs). A URI is a compact sequence of characters that identify an abstract or physical resource, such as an electronic document or web page. A uniform resource locator (URL) is type of URI that specifies the location of the resource on a computer network, and a mechanism for retrieving the resource, such as Hypertext Transfer Protocol (HTTP). An HTTP referrer (also spelled “referer”) is an HTTP header field provided by the resource that identifies the URI that linked to the resource being requested. HTTP header fields are components of the header section of request and response messages. An example of an HTTP referrer field is “Referer: http://www.example.com/home.” By checking the referrer, the new web page can see where the request originated. Although some browsers do not send the referrer from a secure (HTTPS) page, the referrer is generally provided from non-secure (HTTP) pages. Therefore, in the latter cases, the URL is not considered secure.